1. Field of the Invention
The present invention relates to urological warming and cooling devices and more particularly to a warming catheter and method of warming the urethra of a patient during ablative surgery. The apparatus is particularly useful in cryosurgery to prevent damage to tissues surrounding a surgical site from the extremely cold temperatures employed therein. The apparatus is especially useful during transperineal cryoablation of the prostate gland in human males to maintain the temperature of the urethral tissues and thereby prevent urethral sloughing. The apparatus may also have utility where it is desired to lower the temperature of surrounding tissues, such as during laser ablation.
2. Description of the Related Art
Cryosurgical probes are used to treat a variety of diseases. The cryosurgical probes quickly freeze diseased body tissue, causing the tissue to die after which it will be absorbed by the body, expelled by the body or sloughed off. Cryothermal treatment is currently used to treat prostate cancer and benign prostate disease, breast tumors and breast cancer, liver tumors and liver cancer, glaucoma and other eye diseases. Cryosurgery is also proposed for the treatment of a number of other diseases.
The use of cryosurgical probes for cryoablation of the prostate is described in, for example, Onik, Ultrasound-Guided Cryosurgery, Scientific American at 62 (January 1996). Cryosurgical probe systems are manufactured by present assignee, Endocare, Inc. of Irvine, Calif. In cryosurgical ablation procedures generally several cryosurgical probes are inserted through the skin in the perineal area (between the scrotum and the anus), which provides the easiest access to the prostate. The probes are pushed into the prostate gland through previously placed cannulas. Placement of the probes within the prostate gland is typically visualized with an ultrasound imaging probe placed in the rectum. The probes are quickly cooled to temperatures typically below −120° C. The prostate tissue is killed by the freezing, and any tumor or cancer within the prostate is also killed. The body absorbs some of the dead tissue over a period of several weeks. However, other necrosed tissue may slough off and pass through the urethra, often causing undesirable blockage. Thus, it is often desirable to avoid cryoinjury to the urethra during cryoablation of the prostate. This may be done by placing a warming catheter in the urethra and continuously flushing the catheter with warm fluid to keep the urethra from freezing.
Devices for warming the urethra have been available for quite some time. In 1911, U.S. Pat. No. 1,011,606 issued for an “Appliance For Subjecting Portions Of The Human System To Heat Or Cold.” This device was a coaxial dual lumen catheter intended for the application of therapeutic cooling or heating to the urethra and bladder. Devices for warming other body parts have also been proposed, such as U.S. Pat. No. 4,244,377, issued Jan. 13, 1981 to Grams entitled “Ear Probe For Use In Closed-Loop Caloric Irrigation”, which shows a coaxial dual lumen cannula intended for the application of therapeutic heating inside the ear.
U.S. Pat. No. 5,437,673, issued on Aug. 1, 1995 to Baust, et al., entitled “Closed Circulation Tissue Warming Apparatus and Method of Using the Same in Prostate Surgery” illustrates use of a urethral warming catheter which is used to protect the urethra from cryothermal damage during cryosurgical treatment of the prostate for benign prostate hyperplasia. The Baust patent discloses a coaxial three lumen catheter in which warm saline passes through an outside lumen and is returned through a coaxial second lumen. A third lumen is a urinary drainage lumen centrally disposed within the other two lumens. The catheter is used to heat the urethra while the prostate is being frozen with cryosurgical probes.
A very similar device to that disclosed in U.S. Pat. No. 5,437,673 is disclosed in U.S. Pat. No. 5,624,392, issued on Apr. 29, 1997 to Saab, entitled “Heat Transfer Catheter and Methods of Making and Using Same.”
U.S. Pat. No. 5,257,977, issued on Nov. 2, 1993 to Eshel, entitled “Technique for Localized Thermal Treatment of Mammals,” shows a catheter that delivers heated saline flow to provide therapeutic hyperthermia treatment of the prostate. Like the Baust patent, Eshel shows a three lumen catheter with a centrally located urinary drainage lumen.
Still other devices have been described for importing fluid into the body and allowing a means for removing fluid from the body. One such device is described in U.S. Pat. No. 3,087,493, issued Apr. 27, 1960 to Schossow, entitled “Endotracheal Tube”. Schossow describes a device employed to intubate the human trachea. The device is connected with ducts and/or tubes outside the patient for the purpose of, for example, drawing off from the patient's respiratory tract undesirable liquids and/or introducing beneficial liquids into the trachea. The device comprises an outer tube, which fits inside the patient's trachea, and a two layered inner tube. The lumen of the inner tube is open to be connected with devices or ducts through which suction may be applied or fluids injected into the trachea. The distal portion of the inner tube is vented with ports or openings that create a “sprinkler” effect inside the tube.
During cryoablation, the prostate tissue is killed by freezing temperatures in the cryogenic temperature range, typically −120° C. and below. The hot fluid used for the warming catheter is supplied at about 30° C. to 50° C. Warm fluid is pumped through the urethral warming catheter, such as the catheter described in Baust et al. Using this catheter, as the warm fluid travels the length of the urethral catheter disposed within the cryosurgically-cooled urethra, it is cooled by the surrounding freezing tissue. By the time the hot water has traveled from the bladder neck sphincter to the external sphincter, it has been significantly cooled by the surrounding frozen prostate. As a result, the urethral tissue near the bladder neck sphincter (near the hot water outlet) is heated more than the urethral tissue near the external sphincter, creating a strong thermal gradient in the prostatic urethra and an uneven heating effect. By the time the hot water reaches the external sphincter, it may have lost so much heat to the upper region of the urethra that it is not warm enough to protect the external sphincter from freezing. In order for the tissue at the bladder neck sphincter to be adequately warmed, hotter water must be pumped in, risking urethral damage due to scalded tissue, or more water must be pumped at higher rates and pressures, increasing the material requirements of the hot water supply system and the warming catheter.
U.S. Pat. No. 6,017,361, issued to Mikus et al, entitled “Urethral Warming Catheter,” discloses an improved method and means for maintaining the temperature of urethral tissues during cryoablation of the prostate gland and thereby eliminates or reduces the sloughing of dead cells into the urethra. Diffuser holes or ports, much like a “sprinkler,” are drilled into the inner tube of the warming catheter. The holes create an advantage over the prior art of achieving improved uniformity of fluid flow and temperature, utilizing a lower initial temperature and resulting in a more even application of thermal treatment to the urethral tissues. The apparatus may find additional utility in other areas of surgery where thermal treatment or maintenance of tissues is required with or without the capability of drainage.